I have joined just to reply to you OP.
My ‘DH’ left me with a young baby and a toddler.
First thing you need to do is claim UC
as you are now a separate household to your husband as he’s left you.
You do not need a job right now (you already have the hardest job you’ll ever do) and you will not be expected to look for work until your youngest turns 3 so do not listen to previous posters.
He has picked a very stupid time to leave you and the courts will want to see you and the kids housed as their number 1 priority. It will not be 50:50 and the length of the marriage is irrelevant. You will get more as the primary carer.
You need to know exactly what he has got in terms of assets and if you have to do some detective work then do this but do not tell a solicitor where you stumbled across this information.
I represented myself and got enough money (because we had the equity) to buy a house outright with no mortgage and I am eternally grateful for this.
Make a CM claim immediately. He doesn’t legally owe you any money for the kids until you’ve done this.
You have one chance to secure your future for you and the kids and you need to take it. You have to fight and do not be tricked into ‘being fair’. There is nothing fair about the situation he’s left you in.
Lastly, you will be OK. It is extremely difficult at this point and I had to see my GP for medication and counselling. I also had help from a DA charity as he was verbally abusive.
Now I am actually happy and love our new home, life is so so much easier without him around and he has the kids so I get a break.
I also wonder what I ever saw in him. A man that is capable of abandoning a woman with very young children is disgusting.
Good Luck OP.